1. Field of the Invention
The present invention relates to an optical disk device. More specifically, the present invention relates to an optical disk device having an improved clamping mechanism for an optical disk when a DVD-ROM or other optical disk having a composition in which two optical disks are glued together is mounted onto a turntable.
2. Background of the Invention
In recent years, along with the demand for greater recording density, optical disks have come into use in which two optical disks are glued together to form an integrated whole. For example, a so-called one-side readout glued-together disk has been proposed (see, for example, laid open patent application H11-3541, 1999). This is an optical disk in which the information on the two disks can be selectively read by shining a laser beam from one side of one of the laser disks and varying the focal point of the laser beam.
FIGS. 1A and 1B show an outline of an optical disk of this type. FIG. 1A is a cross-sectional view showing an enlargement of the part of an optical disk. As shown in FIG. 1A, optical disk 1 has a first disk 4, which has a first information recording part 3 on one side of a first substrate 2, and a second disk 7 which has a second information recording part 6 on one side of a second substrate 5 opposite first disk 4. First disk 4 and second disk 7 are glued together by a resin layer 8 which consists of ultraviolet-ray-hardened resin, etc.
Optical disk 1 having such a structure is shaped in a donut-disk form as shown in FIG. 1B and has a mounting hole 9 in its center for mounting onto an optical disk device.
An optical disk device for reading information recorded on optical disk 1 of this type or for recording information onto optical disk 1 has a turntable on which to place optical disk 1, and it has a structure by which mounting hole 9 of optical disk 1 is fitted and fixed onto a disk holding part provided in its middle.
FIG. 2A is a cross-sectional view showing an enlargement of the disk holding part in a conventional optical disk device. As shown in FIG. 2A, a conventional optical disk device has on part of the circumferential surface of disk holding part 100 a clamping member 101 that is free to move in the radial direction. The clamping member 101 is at all times urged outward by an urging member such as a coil spring which is not shown.
The surface of clamping member 101 has a mountain shape, and its tip 101a has a pointed angle or a shape with a slight rounding. Therefore optical disk 1 makes contact with the tip 101a at a point or along a line.
That is, when mounting hole 9 of optical disk 1 is fitted onto the disk holding part 100 from above as shown in the diagram, the inner or inside circumferential surface of mounting hole 9 of the optical disk 1 comes into contact with an upper sloping face 101b of clamping member 101, and clamping member 101 moves inward (to the right as shown in the diagram) by the component force of the fitting-in force. When optical disk 1 is fitted in as far as tip 101a of clamping member 101, the inner circumferential surface of the mounting hole 9 comes into contact with tip 101a of clamping member 101 at a point or along a line.
There has been concern that if the gluing-together of the two disks is poor in the optical disk 1 that is thus fitted in as far as tip 101a of clamping member 101. Specifically, if there is a poor gluing-together of the disks 4, 7 in the part near the mounting hole 9, tip 101a of clamping member 101 that makes contact at a point or along a line, exerts a wedge effect, and as shown in FIG. 1B, and it may get in between the first optical disk 4 and second optical disk 7 (where the gluing-together is poor).
As a result, there has been concern that clamping member 101 will peel apart the first optical disk 4 and the second optical disk 7 and expand the region where poor gluing-together occurs, or make the fitting-in of optical disk 1 worse, making it impossible to place optical disk 1 onto the turntable in the correct condition.
An object of this invention, which was devised in consideration of the above-described circumstances, is to provide an optical disk device in which correct positioning onto a turntable can be done for an optical disk having a structure in which two optical disks are glued together, regardless of whether the gluing-together is poor.
This and other objects of the present invention are attained by an optical disk device on which an optical disk is mounted, which optical disk is formed by gluing together a first optical disk and a second optical disk and which has a mounting hole in the middle; the optical disk device comprising a turntable on which the optical disk is placed, a disk holding part that protrudes from the middle of the turntable and onto which fits the mounting hole of the optical disk; and a clamping member provided on part of a circumferential surface in the disk holding part, said clamping member being free to move radially and being impelled radially outward.
The clamping member has a mountain-live shape formed by its first and second sloping faces, and a tip positioned at the boundary of the sloping faces and shaped so as to make a surface contact with the optical disk.
For example, by beveling the tip of the clamping member to be parallel to the mounting direction of the optical disk, the tip of the clamping member can be made to make a surface contact with the optical disk.
Thus by giving the tip of the clamping member a shape that ensures a surface contact with the optical disk, even when the tip comes into contact with the glued-together part of the optical disk, a force that acts on the optical disk is dispersed, the glued-together parts do not peel apart and the clamping member does not get in between the parts, whereby a correct positioning of the optical disk on the turntable is assured.